The disclosures herein relate generally to computer systems and more particularly to heat dissipation for integrated circuits in a portable computer system.
A portable computer is a self-contained personal computer which can be easily moved to and operated at various locations. Portable computers are often referred to as laptop or notebook computers. To be portable, these computers must be small, compact, and lightweight. The conventional portable computer includes a base portion and a lid portion that pivotally opens from the base portion when the portable computer is in use. The lid portion contains a flat panel display such as a liquid crystal display (LCD) or other relatively small display.
Heat distribution is a problem with all computers, especially with portable computers. In the past, heat sinks, heat pipes, and fans have been used to address this problem. One type of heat sink is a metal piece that is thermally coupled to a processor and distributes heat away from the processor. Typically, a heat sink is made of relatively pure aluminum for good thermal conductivity and for reduced weight. Heat sinks add extra pieces to the computer system assembly as well as increasing the complexity of the build and repair operations.
Fans and heat sinks provide a cost effective mechanism for thermally managing many types of portable computer systems. Fans, however, require power and heat sinks require space. While power and space are generally in abundant supply in desktop-type computers, portable computers have a limited supply of both power and space. A commercial advantage is achieved by manufacturing portable computers that are both small and lightweight. Further, portable computers must operate with power conservation in mind. An operating fan may unduly draw upon the batteries of a laptop, making the fan inefficient for long periods of battery-operated use.
Heat pipes are self contained, phase transformation, heat carrying devices, i.e. superconductors of heat. A typical heat pipe may comprise a closed copper tube having a partial vacuum. Liquid in a hot portion of the tube boils at a lower than usual temperature in the partial vacuum. The boiling liquid seeks a cooler spot and thus steam moves to carry heat to the cooler spot where the steam condenses to liquid which returns to the hot end of the tube. The cycle provides a contained circulating heat transfer system.
In U.S. Pat. No. 4,571,456, a portable computer is contained within an outer metal case which physically encapsulates and protects the working components of the computer in the closed, portable configuration. The metal case includes a base which serves as a heat sink for transferring waste heat from heat producing electrical components to the surroundings in the open, operating configuration of the computer. The heat producing components are mounted and located in the base to maximize the transfer of heat to the base. A display housing is pivotally mounted on the base by hinge assemblies for swinging movement between a closed and latched position on the base and an upward and rearwardly inclined angle for viewing by an operator positioned in front of the computer. Stop pins coact with the hinge assemblies for holding the display housing at the desired angle of view, and torsion springs are associated with the hinge assemblies for preventing inadvertent slamming of the display housing against the base during closing. Electrical cables are guided from the base through the hinge assemblies and to the display by cable guides which protect the cables against snagging and unnecessary flexure. A single connector connects an audio circuit on a modem to use either a standard hand set for voice communications or a passive speaker and microphone as an acoustic coupler for data communications.
U.S. Pat. No. 5,513,070 discloses a heat dissipation device for removing heat from a surface mounted integrated circuit component coupled to a printed circuit board in a portable computer. Vias, which are at least partially filled with a heat conductive material, improve heat transfer between a component and a heat conductive block mounted on opposite surfaces of the circuit board. A first section near one end of the heat pipe is attached to the heat conductive block. A second section of the heat pipe is attached to a metal plate which is affixed beneath the keyboard. Heat from the component flows through the vias to the block and is transferred by the heat pipe to the metal plate where it is dissipated.
In U.S. Pat. No. 5, 568,360, a heat transfer system is provided for dissipating thermal energy within the personal computer. The transfer system is designed to move heat from a heat source, such a central processing unit (CPU), to a heatsink arranged upon the portable computer keyboard. The heat transfer mechanism includes a heat slug thermally coupled to the CPU heat source and a heat pipe thermally coupled to a backside surface of a computer keyboard. The heat pipe is designed having minimal thermal gradient, and includes an evaporation/condensation cycle associated with its operation. The heat pipe is preferably orthogonally shaped having at least one flat surface arranged near the intersection of the orthogonal members. The flat section is in registry with a heat source. Movement of the flat section relative to the heat source effectuates abutment and thermal contact therebetween. The present thermal energy transfer system is designed for enhanced heat transfer within a portable computer system without undergoing the disadvantages of bulky finned heatsinks and/or fans.
U.S. Pat. No. 5,598,320 discloses a rotatable and slidable heat pipe apparatus for transferring heat away from a microprocessor chip more rapidly than by heat sink surface area dissipation to the surrounding air alone, comprising a heat sink with an integral cylindrical passageway adapted to receive a first end of a heat pipe shaped like a crankshaft, and a heat spreader formed from a metal plate with a first end rolled up to define a cylindrical opening adapted to receive a second end of the heat pipe. The heat spreader is attached to an underside of a keyboard. Because the heat pipe is able to rotate within the cylindrical passageway and the cylindrical opening, the keyboard can be raised to an open position and lowered to a closed position quickly and simply without the risk of breaking or bending the heat pipe, and manufacturing position tolerances between the heat pipe apparatus components are increased resulting in a simplified manufacturing process. The heat pipe can also be slid into and out of the cylindrical passageway or the cylindrical opening, thereby enabling computer manufacturers to incorporate the heat pipe into portable battery powered notebook-type computer systems designed to allow a user to remove, replace, or swap internal components by simply flipping open or removing the keyboard, and further enabling a user to perform maintenance work or repairs on the computer system without concern for damage to the heat pipe.
U.S. Pat. No. 5,634,351, discloses a two-phase cooling system for a portable computer, the system having an evaporator and a condenser that are both included in either the lid or the base of the computer. The two-phase cooling system is positioned proximate to the computer's heat-producing circuitry, such that the system draws liquid coolant past the circuitry and heat is transferred from the circuitry to the coolant. A fan may also be included to assist in heat rejection from the cooling system. The cooling system includes a flattened heat pipe, with a first side operating as the evaporator and a second side operating as the condenser.
Thermal solutions incorporating heat pipes, heat sinks and fans have become well established in notebook cooling. Heat, traveling from the processor along a heat pipe to a heat sink/radiator, is "actively" removed from the notebook by the air the fan pulls or pushes across the radiator's fins. Traditionally, the components in this type of thermal solution have been located close to the processor in the notebook base. However, as more components crowd into the base of the notebook, the problem of providing a thermal solution sized to adequately handle growing heat loads becomes more difficult.
Therefore, what is needed is an active thermal solution having heat dissipating components located in the lid portion of the portable computer, so that heat generated in the base portion can be routed to the lid and dissipated therefrom without consuming valuable component space in the base portion.